1. Field of the Invention
The present invention generally relates to optical transmission apparatuses, and more particularly to an optical transmission apparatus that is for a wavelength division multiplex (WDM) optical transmission system, and is provided with a wavelength cross-connect (WXC) function and an optical add and drop multiplexing (OADM) function.
2. Description of the Related Art
The WDM optical transmission system is used in a trunk optical network that connects nodes, formed by optical transmission apparatuses set up in a city or the like, via optical transmission lines, and exchanges WDM signal light. The WXC function of the WDM optical transmission system switches an output destination route of signal light input from each route for every wavelength, and sends the signal light to a predetermined route. The OADM function of the WDM optical transmission system adds and sends signal light having an arbitrary wavelength to an arbitrary route, and drops and receives the signal light having the arbitrary wavelength from the arbitrary route. With respect to the WDM optical transmission system, there are demands to enable easy expansion of the system and to enable system construction at a low cost.
In a case where a transmission fault is generated between the nodes of the trunk optical network, there are demands to realize a function that instantaneously switches the transmission route between the nodes to an alternative route and instantaneously switches the signal light to a signal light having a wavelength usable in the alternative route. In order to realize this function, there is active research and development of devices that can form a route switching means, such as a wavelength selective switch (WSS) that can switch and output input signal light having an arbitrary wavelength to an arbitrary route, and a wavelength blocker that can block signal light having an arbitrary wavelength from passing through from among input WDM signal light, to be used in place of an optical matrix switch having a number of input ports equal to a product of the number of input routes and the number of wavelengths and having a number of output ports equal to a product of the number of output routes and the number of wavelengths.
FIG. 1 is a system block diagram showing a structure of an example of a conventional optical transmission apparatus applied with the WSS. FIG. 1 shows a case where the number of routes is 4, and the number of wavelengths (that is, channels) of the signal light is 40. As shown in FIG. 1, the optical transmission apparatus has, in a core portion thereof, first through fourth input wavelength selective switches (1×4 WSSs) 6-11 through 6-14 having 1 input port and 4 output ports, and first through fourth output wavelength selective switches (4×1 WSSs) 6-21 through 6-24 having 4 input ports and 1 output port.
The signal light from a first route R#1 is input to the input port of the first input wavelength selective switch (1×4 WSS) 6-11, and the signal lights from the output ports of the first input wavelength selective switch (1×4 WSS) 6-11 are output to the input ports of the output wavelength selective switches (4×1 WSSs) 6-22, 6-23 and 6-24 for the routes R#2, R#3 and R#4, other than the route R#1, and to an optical demultiplexer 6-41 of a first signal drop port D#1.
Similarly, the signal light from the second route R#2 is input to the input port of the second input wavelength selective switch (1×4 WSS) 6-12, and the signal lights from the output ports of the second input wavelength selective switch (1×4 WSS) 6-12 are output to the input ports of the output wavelength selective switches (4×1 WSSs) 6-21, 6-23 and 6-24 for routes R#1, R#3 and R#4, other than the route R#2, and to an optical demultiplexer 6-42 of a second signal drop port D#2.
Similarly, the signal light from the third route R#3 is input to the input port of the third input wavelength selective switch (1×4 WSS) 6-13, and the signal lights from the output ports of the third input wavelength selective switch (1×4 WSS) 6-13 are output to the input ports of the output wavelength selective switches (4×1 WSSs) 6-21, 6-22 and 6-24 for routes R#1, R#2 and R#4, other than the route R#3, and to an optical demultiplexer 6-43 of a third signal drop port D#3.
Similarly, the signal light from the fourth route R#4 is input to the input port of the fourth input wavelength selective switch (1×4 WSS) 6-14, and the signal lights from the output ports of the fourth input wavelength selective switch (1×4 WSS) 6-14 are output to the input ports of the output wavelength selective switches (4×1 WSSs) 6-21, 6-22 and 6-23 for routes R#1, R#2 and R#3, other than the route R#4, and to an optical demultiplexer 6-44 of a fourth signal drop port D#4.
On the other hand, the input ports of the first output wavelength selective switch (4×1 WSS) 6-21 receives the signal lights from the output ports of the input wavelength selective switches (1×4 WSSs) 6-12, 6-13 and 6-14 for the routes R#2, R#3 and R#4, other than the route R#1, and the signal light from an optical multiplexer 6-31 of a first signal add port A#1.
Similarly, the input ports of the second output wavelength selective switch (4×1 WSS) 6-22 receives the signal lights from the output ports of the input wavelength selective switches (1×4 WSSs) 6-11, 6-13 and 6-14 for the routes R#1, R#3 and R#4, other than the route R#2, and the signal light from an optical multiplexer 6-32 of a second signal add port A#2.
Similarly, the input ports of the third output wavelength selective switch (4×1 WSS) 6-23 receives the signal lights from the output ports of the input wavelength selective switches (1×4 WSSs) 6-11, 6-12 and 6-14 for the routes R#1, R#2 and R#4, other than the route R#3, and the signal light from an optical multiplexer 6-33 of a third signal add port A#3.
Similarly, the input ports of the fourth output wavelength selective switch (4×1 WSS) 6-24 receives the signal lights from the output ports of the input wavelength selective switches (1×4 WSSs) 6-11, 6-12 and 6-13 for the routes R#1, R#2 and R#3, other than the route R#4, and the signal light from an optical multiplexer 6-34 of a fourth signal add port A#4.
According to the structure shown in FIG. 1, the output route to which the signal light is added is fixed for each of the first through fourth signal add ports A#1 through A#4. In other words, the first signal add port A#1 can only add the signal light to the output route R#1, and the second signal add port A#2 can only add the signal light to the output route R#2. Similarly, the third signal add port A#3 can only add the signal light to the output route R#3, and the fourth signal add port A#4 can only add the signal light to the output route R#4.
In addition, the input route from which the signal light is dropped is fixed for each of the first through fourth signal drop ports D#1 through D#4. In other words, the first signal drop port D#1 can only drop the signal light from the optical route R#1, and the second signal drop port D#2 can only drop the signal light from the optical route R#2. Similarly, the third signal drop port D#3 can only drop the signal light from the optical route R#3, and the fourth signal drop port D#4 can only drop the signal light from the optical route R#4.
For this reason, each of the first through fourth signal add ports A#1 through A#4 cannot add and send the signal light to an arbitrary output route, and each of the first through fourth signal drop ports D#1 through D#4 cannot drop and receive the signal light from an arbitrary input route. In other words, it is not possible to realize the OADM function with respect to arbitrary routes by an arbitrary signal add port and an arbitrary signal drop port.
Moreover, according to the structure shown in FIG. 1, each of the signal add ports A#1 through A#4 uses 40 transmitters TX for sending the signal lights having the fixed wavelengths of λ1 through λ40, and the outputs of the transmitters TX corresponding to the wavelengths of the signal lights to be added are multiplexed by the optical multiplexers 6-31 through 6-34. Furthermore, each of the signal drop ports D#1 through D#4 uses 40 receivers RX for receiving the signal lights having the fixed wavelengths of λ1 through λ40, and the signal lights are branched by the optical demultiplexers 6-41 through 6-44 and received by the receivers RX. It is thus necessary to provide expensive WDM optical amplifiers 6-51 through 6-54 and 6-61 through 6-64, in order to compensate for the large losses at the optical multiplexers 6-31 through 6-34 and the optical demultiplexers 6-41 through 6-44.
A Japanese Laid-Open Patent Application No. 2006-140598, having a corresponding U.S. patent application Publication No. US2006/0098981, proposes an optical transmission apparatus which uses a wavelength selective switch in the signal add port and the signal drop port of the structure shown in FIG. 1, so as to enable adding and dropping of the signal light having an arbitrary wavelength with respect to an arbitrary route. According to this proposal, multiplexers are used in place of the output wavelength selective switches (4×1 WSSs) 6-21 through 6-24 shown in FIG. 1.
In addition, a Japanese Laid-Open Patent Application No. 2006-87062, having a corresponding U.S. patent application Publication No. US2006/0034610, proposes an optical add and drop apparatus which has a through route for passing the input light from the input port to the output port, a drop output port for dropping the input light having a predetermined wavelength, and an add output port for adding the signal light having a predetermined wavelength to the input light. According to this proposal, it is possible to easily expand the number of wavelengths and expand easily expand the wavelength cross-connect function, and to add and drop the signal lights without breaking the transmission signal.
FIG. 2 is a system block diagram showing a structure of an example of a conceivable optical transmission apparatus. This second example shown in FIG. 2 uses the wavelength selective switch in the signal add port and the signal drop port of the structure shown in FIG. 1, and the input wavelength selective switch and the output wavelength selective switch for each of the routes, so that it is possible to switch the route of and to drop or add the signal light having an arbitrary wavelength with respect to an arbitrary route.
FIG. 2 shows a case where the number of routes is 4, and the number of wavelengths (that is, channels) of the signal light is 40, similarly to the case shown in FIG. 1. As shown in FIG. 2, the optical transmission apparatus has, in a core portion thereof, first through fourth input wavelength selective switches (1×7 WSSs) 7-11 through 7-14 having 1 input port and 7 output ports, and first through fourth output wavelength selective switches (7×1 WSSs) 7-21 through 7-24 having 7 input ports and 1 output port.
The signal light from the first route R#1 is input to the input port of the first input wavelength selective switch (1×7 WSS) 7-11, and the signal lights from the output ports of the first input wavelength selective switch (1×7 WSS) 7-11 are output to the input ports of the output wavelength selective switches (7×1 WSSs) 7-22, 7-23 and 7-24 for the routes R#2, R#3 and R#4, other than the route R#1, and to wavelength selective switches (4×1 WSSs) 7-41 through 7-44 of first through fourth signal drop ports D#1 through D#4.
Similarly, the signal light from the second route R#2 is input to the input port of the second input wavelength selective switch (1×7 WSS) 7-12, and the signal lights from the output ports of the second input wavelength selective switch (1×7 WSS) 7-12 are output to the input ports of the output wavelength selective switches (7×1 WSSs) 7-21, 7-23 and 7-24 for routes R#1, R#3 and R#4, other than the route R#2, and to the wavelength selective switches (4×1 WSSs) 7-41 through 7-44 of the first through fourth signal drop ports D#1 through D#4.
Similarly, the signal light from the third route R#3 is input to the input port of the third input wavelength selective switch (1×7 WSS) 7-13, and the signal lights from the output ports of the third input wavelength selective switch (1×7 WSS) 7-13 are output to the input ports of the output wavelength selective switches (7×1 WSSs) 7-21, 7-22 and 7-24 for routes R#1, R#2 and R#4, other than the route R#3, and to the wavelength selective switches (4×1 WSSs) 7-41 through 7-44 of the first through fourth signal drop ports D#1 through D#4.
Similarly, the signal light from the fourth route R#4 is input to the input port of the fourth input wavelength selective switch (1×7 WSS) 7-14, and the signal lights from the output ports of the fourth input wavelength selective switch (1×7 WSS) 7-14 are output to the input ports of the output wavelength selective switches (7×1 WSSs) 7-21, 7-22 and 7-23 for routes R#1, R#2 and R#3, other than the route R#4, and to the wavelength selective switches (4×1 WSSs) 7-41 through 7-44 of the first through fourth signal drop ports D#1 through D#4.
On the other hand, the input ports of the first output wavelength selective switch (7×1 WSS) 7-21 receives the signal lights from the output ports of the input wavelength selective switches (1×7 WSSs) 7-12, 7-13 and 7-14 for the routes R#2, R#3 and R#4, other than the route R#1, and the signal lights from the wavelength selective switches (1×4 WSSs) 7-31 through 7-34 of the first through fourth signal add ports A#1 through A#4.
Similarly, the input ports of the second output wavelength selective switch (7×1 WSS) 7-22 receives the signal lights from the output ports of the input wavelength selective switches (1×7 WSSs) 7-11, 7-13 and 7-14 for the routes R#1, R#3 and R#4, other than the route R#2, and the signal lights from the signal lights from the wavelength selective switches (1×4 WSSs) 7-31 through 7-34 of the first through fourth signal add ports A#1 through A#4.
Similarly, the input ports of the third output wavelength selective switch (7×1 WSS) 7-23 receives the signal lights from the output ports of the input wavelength selective switches (1×7 WSSs) 7-11, 7-12 and 7-14 for the routes R#1, R#2 and R#4, other than the route R#3, and the signal lights from the wavelength selective switches (1×4 WSSs) 7-31 through 7-34 of the first through fourth signal add ports A#1 through A#4.
Similarly, the input ports of the fourth output wavelength selective switch (7×1 WSS) 7-24 receives the signal lights from the output ports of the input wavelength selective switches (1×7 WSSs) 7-11, 7-12 and 7-13 for the routes R#1, R#2 and R#3, other than the route R#4, and the signal lights from the wavelength selective switches (1×4 WSSs) 7-31 through 7-34 of the first through fourth signal add ports A#1 through A#4.
The first signal add port A#1 has 40 variable wavelength transmitters TX for sending signal lights having 40 different wavelengths, a 2-stage switch, made up of wavelength selective switches (7×1 WSSs) 7-51 and 7-61, for selectively inputting the signal light from the variable wavelength transmitters TX, and a wavelength selective switch (1×4 WSS) 7-31. The second signal add port A#2 has 40 variable wavelength transmitters TX for sending signal lights having 40 different wavelengths, a 2-stage switch, made up of wavelength selective switches (7×1 WSSs) 7-52 and 7-62, for selectively inputting the signal light from the variable wavelength transmitters TX, and a wavelength selective switch (1×4 WSS) 7-32. The third signal add port A#3 has 40 variable wavelength transmitters TX for sending signal lights having 40 different wavelengths, a 2-stage switch, made up of wavelength selective switches (7×1 WSSs) 7-53 and 7-63, for selectively inputting the signal light from the variable wavelength transmitters TX, and a wavelength selective switch (1×4 WSS) 7-33. The fourth signal add port A#4 has 40 variable wavelength transmitters TX for sending signal lights having 40 different wavelengths, a 2-stage switch, made up of wavelength selective switches (7×1 WSSs) 7-54 and 7-64, for selectively inputting the signal light from the variable wavelength transmitters TX, and a wavelength selective switch (1×4 WSS) 7-34.
In addition, the first signal drop port D#1 has a wavelength selective switch (4×1 WSS) 7-41, a 2-stage switch, made up of wavelength selective switches (1×7 WSSs) 7-71 and 7-81, and 40 receivers RX for receiving signal lights having 40 different wavelengths. The second signal drop port D#2 has a wavelength selective switch (4×1 WSS) 7-42, a 2-stage switch, made up of wavelength selective switches (1×7 WSSs) 7-72 and 7-82, and 40 receivers RX for receiving signal lights having 40 different wavelengths. The third signal drop port D#3 has a wavelength selective switch (4×1 WSS) 7-43, a 2-stage switch, made up of wavelength selective switches (1×7 WSSs) 7-73 and 7-83, and 40 receivers RX for receiving signal lights having 40 different wavelengths. The fourth signal drop port D#4 has a wavelength selective switch (4×1 WSS) 7-44, a 2-stage switch, made up of wavelength selective switches (1×7 WSSs) 7-74 and 7-84, and 40 receivers RX for receiving signal lights having 40 different wavelengths.
Each of the first through fourth signal add ports A#1 through A#4 can arbitrarily select the output route to which the signal light is to be added, from each of output routes R#1out, R#2out, R#3out and R#4out. In addition each of the first through fourth signal drop ports D#1 through D#4 can arbitrarily select the input route from which the signal light is to be dropped, from each of input routes R#1in, R#2in, R#3in and R#4in.
In the optical transmission apparatus shown in FIG. 2, when the number of routes is increased or decreased, the number of wavelength selective switches (WSSs) 7-11 through 7-14 and 7-21 through 7-24 corresponding to each route must be increased or decreased, and the number of ports of the wavelength selective switches (WSSs) 7-11 through 7-14 and 7-21 through 7-24 corresponding to each route, the wavelength selective switches (WSSs) 7-31 through 7-34 in each signal add port and the wavelength selective switches (WSSs) 7-41 through 7-44 in each signal drop port must be increased or decreased.
In addition, when the number of wavelengths (that is, channels) is increased or decreased, the number of ports of the wavelength selective switches (7×1 WSSs) 7-51 through 7-54 and 7-61 through 7-64 for selecting the signal lights from the transmitters TX of the signal add ports A#1 through A#4 and outputting the selected signal lights to the input ports of the wavelength selective switches (1×4 WSSs) 7-31 through 7-34 must be increased or decreased, and the number of ports of the wavelength selective switches (1×7 WSSs) 7-71 through 7-74 and 7-81 through 7-84 for selecting the signal lights from the output ports of the wavelength selective switches (4×1 WSSs) 7-41 through 7-44 and outputting the selected signal lights to the receivers RX of the signal drop ports D#1 through D#4.
Therefore, according to the structure shown in FIG. 2, it is possible to add the signal light having an arbitrary wavelength with respect to an arbitrary signal add port and to drop the signal light having an arbitrary wavelength from an arbitrary signal drop port, but compared to the structure shown in FIG. 1, there were problems in that the number of required wavelength selective switches (WSSs) and the number of ports thereof increase considerably, that the number of wirings which couple the wavelength selective switches (WSSs) increases in a geometric series, and that the cost and the scale of the optical transmission apparatus increase.